Conventional semiconductor wafer cleaning apparatus suffers from a variety of general drawbacks. These include less than desired production throughput; excessive downtime for maintenance; inadequately clean wafers due to inefficient surface scrubbing, contaminant removal, and debris removal; excessive wafer breakage; lack of flexibility of configuration and control to handle a variety of wafer sizes and geometries; excessive consumption of processing fluids and other consumables; excessive generation of emissions and other industrial wastes; and excessive demand on manufacturing floor space.
Conventional wafer cleaning apparatus normally uses PVA (Polyvinyl Alcohol) sponges as the cleaning elements. Conventional wafer cleaning machines present several sponge related problems, including relatively short sponge service life due to particle buildup and excessive downtime and handling requirements in conventional sponge replacement, leading to long process requalification time. Moreover, conventional sponges are stretched onto a single shaft, which is normally oversized in order to avoid slippage between the sponge and the shaft under load.
The stretching of a sponge over a single oversized shaft in the prior art is a difficult operation and typically results in the surface of the sponge becoming lumpy and unevenly distributed on the shaft. The resulting uneven sponge distribution often leads to non-uniform contact pressure between a rotating sponge and wafer, increasing the risk of wafer breakage. Such nonuniformity and lumpiness impede the ability of the sponge to uniformly clean a wafer surface. Moreover the inability to have a repeatable surface texture when sponges are replaced on the core degrades the ability to predict the results of the cleaning process. Additionally, single-shaft mounted sponges on conventional machines are generally not efficiently rinsed, leading to contaminant buildup on the wafer and further contributing to shortened sponge life. Some cleaning equipment manufacturers rinse the sponge from the inside through a single shaft, requiring rotary fluid feedthroughs.
Conventional wafer cleaning apparatus generally operates with the plane of the wafer oriented horizontally. This horizontal orientation occupies more floor space than is desirable and is typically difficult to maintain, adversely affecting throughput. Horizontal wafer orientation further impedes efficient flushing away of contaminants and debris. Gill U.S. Pat. No. 5,624,501 describes a wafer cleaning apparatus with vertically wafer orientation and two-sided brush cleaning, in which the opposed brushes are conically shaped. Kudo et al. U.S. Pat. No. 5,547,515 describes a wafer cleaning method with vertically oriented wafers and simultaneous two-sided brush cleaning between counter-rotating tubular shaped brushes mounted on single shafts in a bath. Jones et al. U.S. Pat. No. 5,486,134 describes a method for texturing magnetic data storage disks, wherein the disk is oriented vertically between counter-rotating tubular shaped brushes mounted on single shafts and rotating in an upward direction along their respective lines of contact with the disk. Thrasher et al. U.S. Pat. No. 5,475,889 describes a brush assembly for cleaning horizontally oriented wafers between tubular shaped counter-rotating brushes, wherein the brushes are mounted respectively on single shafts. Holley et al. U.S. Pat. No. 5,639,311 describes a method for cleaning horizontally oriented wafers between tubular shaped counter-rotating brushes, wherein the brushes are mounted respectively on single shafts and are irrigated internally with cleaning fluids. Akimoto U.S. Pat. No. 5,361,449 describes apparatus for cleaning horizontally oriented stationary wafers on the bottom surface only, using a planetary mounted brush rotating in a plane parallel to the wafer surface. Convac GmbH (Germany) previously used a horizontally oriented non-interchangeable wafer mounting ring for double-sided wafer cleaning.
Many conventional wafer cleaning systems support and rotate the wafer on its circumference using two or three grooved rolls. This drive arrangement is, however, subject to slippage, which may generate contaminant particles and stresses that lead to wafer breakage. The conventional wafer support and drive arrangement is also difficult to adapt to a variety of wafer sizes and shapes. Particularly, it is difficult to support and rotate wafers having flats or notches on their edges without generating mechanical shocks that increase the risk of wafer breakage.
Conventional wafer drying apparatus frequently involves wafer spin/rinse cycles in which the wafers are mechanically moved, increasing the risk of breakage. In addition, high drying temperatures encountered in some wafer dryers may generate thermal stresses that further aggravate the risk of wafer breakage. Also, the spin/rinse cycles may damage photoresist on patterned resist wafers. McConnell et al. U.S. Pat. No. 4,911,761 and Mohindra et al. U.S. Pat. No. 5,571,337 describe processes for drying without spinning, involving immersion in a rinse fluid followed by displacement of the rinse fluid by a drying vapor. Bran U.S. Pat. No. 5,539,995 describes a system for wafer drying without spinning, involving exposure of the wafer to a flowing vapor stream. Bran U.S. Pat. No. 5,556,479 describes a method and apparatus for wafer drying without spinning, involving immersion in a rinse fluid that is subsequently displaced by a drying vapor, in which the wafer surface is heated radiantly. Several equipment manufacturers, for example Verteq Inc. of Santa Ana, Calif. USA; YieldUP International of 117 Easy Street, Mountain View, Calif. USA 94043 (see for example bulletin D0013-6/96E), and Steag Microtech, of Germany offer a "MARANGONI" type rinse/dry system in which the wafer remains motionless during the procedure and is dried using low-temperature dilute amounts of isopropyl alcohol in a nitrogen carrier gas. Although this system reduces wafer breakage and chemical consumption, it typically involves relatively large processing chambers, and thus could benefit from further reduction in size to reduce chemical consumption and manufacturing floor space demands.
Conventional wafer cleaning transport assemblies are cumbersome, poorly integrated into process requirements and apparatus, subject to contamination, and excessively demanding of manufacturing floor space. Some wafer transport assemblies require wafers to be transported singly or collectively in cassettes or baskets. Thietje U.S. Pat. No. 5,468,302 describes a wafer transport assembly, wherein vertically oriented wafers are individually moved between process stations using a pair of independent robotic devices sliding on a common rail. Lutz U.S. Pat. No. 5,529,638 describes a wafer transport method, wherein wafers are individually floated along a fluid track. Kudo et al. U.S. Pat. No. 5,547,515 describes a method for wafer transport, wherein wafer edges are gripped between elastically deformable arms that move linearly with respect to each other to engage and release the wafer edges.
Accordingly the art needs a semiconductor cleaning and drying apparatus having increased production throughput; lower downtime for maintenance; more efficient contamination control, surface scrubbing, and debris removal; reduced wafer breakage; greater flexibility of configuration and control to handle a larger variety of wafer sizes and geometries; lower consumption of processing fluids and other consumables; lower generation of emissions and other industrial wastes; and lower demand on manufacturing floor space.
Particularly, the art needs a new sponge assembly configuration that reduces handling, eliminates distortion of the sponge, promotes efficient rinsing and flushing of particles and other contaminants, and increases service life between sponge replacements. Also needed is an apparatus to overcome the drawbacks in conventional horizontal wafer support and rotation arrangements, including limited brush access, inefficient rinsing and flushing, drive slippage and particle generation, and limitations in sizes and shapes of wafers that can be accommodated. Further needed is a rinse/dry apparatus that minimizes floor space requirements and process chemical consumption, at the same time keeping the wafer motionless and avoiding high temperatures. Additionally needed is a wafer transport apparatus occupying a minimal footprint, capable of efficiently transferring multiple wafers simultaneously among multiple process sites.